1. FIELD OF THE INVENTION
The present invention relates to an electrically conducting device for use with an electrode roller and, in particular, to an electrically conducting device for use with an electrode roller which is used to apply a corona discharge for activation of the surface of a web (paper, plastic sheet or the like) employed as a photographic film base or the like, or to make uniform the electrostatic charge that is generated on the surface of the web due to the corona activation or the like.
2. DESCRIPTION OF THE RELATED ART
Some of the webs for use in photography have a surface which can be hydrophobic. For example, the surface of a photographic paper can be coated with a polymer film and a polymer, so that the paper surface can be additionally provided with a water proof property and the like, that is, it becomes hydrophobic. However, in order that a photographic emulsion, especially, a gelatino-silver halide emulsion or the like can be adhered to the photographic paper, the paper surface must by hydrophilic. For this reason, in the case of the photographic paper with the polymer coated thereto, a strong corona discharge is applied to the surface of the paper so that it is activated, that is, the paper surface becomes hydrophilic. Also, when such corona discharge is effected, then there is developed an irregular electrostatic charge on the surface of the coated polymer. The irregular static charge makes it impossible for the emulsion to be coated uniformly. In view of this, the irregular static charge must be removed from the surface of the photographic paper or must be controlled into a uniform one before the paper surface is coated with the emulsion.
When the corona discharge is applied to the abovementioned hydrophobic photographic paper surface or the like, or when the irregular static charge is controlled into the uniform static charge, an electrode roller is used.
In FIG. 5, there is shown a flow diagram of a corona discharge treatment or a static charge uniforming treatment on the surface of a photographic paper by use of an electrode roller, which is disclosed in U.S. Pat. No. 3,531,314 patented on Sept. 29, 1970. As shown in FIG. 5, a web 50, which is treated by a corona discharge or on which a static charge is made uniform is supplied from a roller 52. The web 50 is brought into sliding contact with an electrode roller 54, rollers 56, 58, an electrode roller 60 and a delivery roller 62 in this order through which the web 50 is transported and treated at the high speed. The electrode roller 54 has a main body 55 which is composed of an electrically conducting material, and also has a rotary shaft 64 which is grounded. Above the electrode roller 54 there is arranged a discharge electrode 68 which is connected to a power source 66, and a corona discharge is applied between the discharge electrode 68 and the electrode roller 54.
Another electrode roller 60, which is arranged downstream in FIG. 5, has a main body 61 which is also composed of an electrically conducting material and also has a rotary shaft 69 which is connected to another power source 71 and to which a voltage of 500 to 50,000 volts is applied. And, below the electrode roller 60 there is disposed a knife-shaped electrode 73 which is grounded. In this structure, a given voltage is applied across the electrode roller 60 and the knife-shaped electrode 73.
In the above-mentioned construction, the web 50 is brought into sliding contact with the electrode rollers 54 and 60 at a speed of 15 to 180 m/min. (50 to 600 fpm) or higher before it is fed out. When the web 50 is brought into sliding contact with the electrode roller 54, the surface of web 50 is activated by a corona discharge so that it becomes hydrophilic. Also, when the web 50 is brought into sliding contact with the electrode roller 60, the irregularities of the static charges on the web surface are controlled to be uniform. By means of the above-mentioned corona activation and static charge uniforming treatments, the web can be coated with a photographic emulsion with good adherence in the following stage.
By the way, in a conventional electrode roller, when the roller is made to conduct with respect to a grounding surface or a power source, an electric brush is brought into sliding contact with the rotary shaft thereof and is also connected with a power terminal or the grounding surface. FIGS. 6(a) and (b) are respectively a side view and a section view to illustrate the connection portions between the electrode roller and brush in the prior art. The electrode roller has a rotary shaft 70 over which an electrically conductive ring member 72 is fitted and secured, and a pair of electric brushes 74, 74 are in sliding contact with the outer peripheral surface of the ring member 72. The pair of electric brushes 74, 74 are mounted to the leading ends of a pair of arms 78, 78 of a holding device 76, respectively. Each of the arms 78, 78 is rotatably mounted through a pin 89 to the main body of the holding device 76. The main body of the holding device 76 is provided with a metal fitting member 82 and there are provided springs 84, 84 respectively between the metal fitting member 82 and the middle portions of the arms 78, 78. The springs 84, 84 respectively energize the pair of arms 78, 78 in the directions of shown arrows, and the electric brushes 74, 74 are brought into sliding contact with the outer peripheral surface of the ring member 72. The main body of the holding device 76 and the arms 78 are respectively formed of an electrically conductive material, and the main body of the holding device 76 is connected to a terminal of a power supply unit or to the ground, although not shown. Thanks to this, while rotating, the electrode roller is caused to conduct with respect to the power supply unit or the ground through the rotary shaft 70, ring member 72 and electric brushes 74, so that the irregular static charge developed on the surface of the web or the like in sliding contact with the above-mentioned electrode roller can be controlled into a uniform static charge.
However, in the above-mentioned conventional electrically conducting device for use with the electrode roller, since the electric brush 74 is brought into sliding contact with the ring member 72 in such a manner that it is energized by the spring 84, if the electrode roller is rotated at high speeds, then the electric brush 74 is caused to wear heavily and generate powdered dust to thereby pollute its environment, so that a reliability on the conduction of the roller with respect to the outer peripheral surface of the ring member 72 is unfavorably reduced.